The object of experiments proposed here is to clarify the behavioral and biological means by which developing mammals adapt to changes in the olfactory environment. The first experiment proposed will investigate the possibility that familiar odor cues elicit nursing by rat pups. Neonates will be required to approach one of two anesthesized lactating females nourished with differently scented solutions. The second experiment proposed will investigate the possibility that changes in the anatomy of the olfactory bulb underlie odor preference changes in postweanling rats. It will examine odor preferences and mitral cell morphology in juvenile rats following exposure to pure chemical or complex organic odors.